The present invention relates to a method for making aromatic organic carbonates such as diphenyl carbonate by effecting reaction between an aromatic organic hydroxy compound, such as phenol, and carbon monoxide and oxygen in the presence of an effective amount of a palladium carbonylation catalyst. More particularly, the present invention relates to the carbonylation of an aromatic organic hydroxy compound utilizing an organic cocatalyst, such as a terpyridine in combination with the palladium carbonylation catalyst.
Procedures for making diorganic carbonates are shown by Hallgren, U.S. Pat. Nos. 4,361,519 and 4,410,464, utilizing a molecular sieve as a drying agent for the water formed during the reaction. A procedure for making aromatic organic carbonates by catalytic carbonylation is shown by Japanese patent 01,165,551. Aromatic organic carbonates are of particular interest to thermoplastic manufacturers, since they offer an alternative non-phosgene route to aromatic polycarbonates by melt transesterification. A procedure for making aromatic organic carbonates using an organic solvent, such as methylene chloride, is shown by Chalk, U.S. Pat. No. 4,187,242. Reference also is made to T. C. Chang in EPA 8911158.8, Jun. 26, 1989, and EP350-700-A, utilizing a divalent or trivalent manganese salt, or cobalt (II) salt in combination with hydroquinone and a palladium catalyst, to catalyze the conversion of an aromatic organic hydroxy compound, such as phenol, to an aromatic organic carbonate. U.S. Pat. No. 4,218,391, Romano et al employ a copper salt to prepare organic esters of carbonic acid. Attempts to use such catalyst with aromatic organic hydroxy compounds, such as phenol, under constant flow conditions have been found to provide unsatisfactory results with respect to % carbonate yields and % carbonate selectivity as compared to the use of aliphatic hydroxy compounds, such as methanol, in preparing aliphatic carbonates under substantially the same conditions.
In application EP350-700-A and copending application Ser. No. 07/906,681, carbonylation of aromatic organic hydroxy compound was achieved utilizing a divalent or trivalent manganese salt or cobalt (II) salts and organic cococatalyst such as hydroquinone or benzoquinone in combination with a palladium catalyst. Although the aforementioned cocatalyst system provides improved yields of aromatic organic carbonate as a result of the carbonylation of aromatic organic hydroxy compounds, organic cocatalyst, such as benzoquinone has to be utilized in the range of 10-40 equivalents per equivalent of palladium, to show a reasonable rate of aromatic organic carbonate production. In addition it has been found that benzoquinone organic cocatalyst based systems are often readily degraded resulting in the production of color bodies and reduced catalyst stability following exposure to ambient conditions. As a result it was not feasible to recycle palladium carbonylation catalyst used in the manufacture of aromatic organic carbonates at elevated conditions of temperature and pressure and there after allow the introduction of make-up aromatic organic hydroxy compound into the reactor under ambient conditions.